1. Field of the Invention
The present invention relates to a flat panel display, and more particularly, to a flat panel display and a method of fabricating the same with improved adhesive strength of an upper plate and a lower plate.
2. Description of the Related Art
Recently, various flat panel display devices have been highlighted with reduced weight and bulk to eliminate disadvantages of cathode ray tube (CRT) technology. Such flat panel display devices include liquid crystal display (LCD) devices, field emission display (FED) devices, plasma display panel (PDP) devices, an electro-luminescence (EL) displays, etc. Among these flat panel display devices, an LCD controls the light transmittance of liquid crystal cells in accordance with video signals to display a picture, which corresponds to the video signals, in a liquid crystal display panel where the liquid crystal cells are arranged in a matrix shape. In this case, a thin film transistor TFT is generally used as a switching device to independently supply the video signals to each liquid crystal cell.
FIG. 1 shows a related art liquid crystal display panel.
As shown in FIG. 1, the related art liquid crystal display panel includes an upper plate in which a black matrix 2, a color filter 6, a pattern spacer 13 and an upper alignment film 8 are sequentially formed on an upper substrate 1; a lower plate in which a thin film transistor TFT, a common electrode 4, a pixel electrode 9, and a lower alignment film 10 are formed on a lower substrate 5; and a liquid crystal material (not shown) injected into an inner space between the upper plate and the lower plate.
In the upper plate, the black matrix 2 is formed overlapping the area of the TFT on the lower substrate 5 and the areas of the gate and data lines (not shown). The black matrix 2 also partitions the cell regions at which the color filter 6 is to be formed. The black matrix 2 prevents light leakage and absorbs external light, thereby improving the contrast ratio. The color filter 6 is formed at the cell region partitioned by the black matrix 2 and is formed over the black matrix 2. The color filter 6 is formed for each of red (R), green (G), and blue (B) filters to produce red, green, and blue colors. The pattern spacer 13 maintains the cell gap between the upper substrate 1 and the lower substrate 5.
In the lower plate, the TFT includes a gate electrode 16 with a gate line (not shown) formed on the lower substrate 5; semiconductor layers 126 and 127 formed overlapping the gate electrode 16 with a gate insulating layer 129 positioned therebetween; and source/drain electrodes 128 and 130 formed with a data line (not shown) with the semiconductor layers 126 and 127 positioned therebetween. The TFT supplies pixel signals from the data line to the pixel electrode 9 in response to scan signals from the gate line. The pixel electrode 9 is made of a transparent conductive material with a high light transmittance and contacts the drain electrode 130 of the TFT with a passivation film 25 positioned therebetween. The common electrode 4 is formed in a stripe form to alternate with the pixel electrode 9. A common voltage being a reference to drive the liquid crystal material is applied to the common electrode 4. In an in-plane switching (IPS) mode liquid crystal display panel, a horizontal electric field formed by the common voltage and a pixel voltage supplied to the pixel electrode 9 makes the liquid crystal molecules rotate in a horizontal direction.
In a twisted nematic (TN) liquid crystal display panel, the common electrode is formed on the upper plate. In this case, a vertical electric field formed by the common voltage applied to the common electrode and the pixel electrode applied to the pixel electrode makes the liquid crystal material rotate in a vertical direction. An upper alignment film 8 and a lower alignment film 10 for aligning a liquid crystal material are formed by applying an alignment material such as polyimide to perform a rubbing process. Then, the complicated upper and lower substrates 1 and 5 are combined with each other such that the upper and the lower alignment films 8 and 10 directly contact each other near the area of the pattern spacer 13 of the upper substrate 1. The pattern spacer 13 of the upper substrate maintains the cell gap between the two substrates.
However, the polyimide used for the material of the upper and the lower alignment films 8 and 10 has a relatively weak adhesive strength. Accordingly, when liquid crystal material is over-injected into the space between the upper plate 40 and the lower plate 50, the upper plate 40 becomes separated from the lower plate 50, as shown in FIG. 2. As a result, the alignment of the liquid crystal material becomes scattered by the separated space. Furthermore, when the liquid crystal display panel receives an impact from an exterior, the upper plate 40 and the lower plate 50 having such weak adhesion properties are easily separated from each other.